An arrangement of this kind is known from German patent application DE 101 51 778 A1. In the arrangement described in that publication, first of all a magnetic selection field having a spatial distribution of the magnetic field strength is generated such that a first sub-zone having a relatively low magnetic field strength and a second sub-zone having a relatively high magnetic field strength are formed in the examination zone. The position in space of the sub-zones in the examination zone is then shifted, so that the magnetization of the particles in the examination zone changes locally. Signals are recorded which are dependent on the magnetization in the examination zone, which magnetization has been influenced by the shift in the position in space of the sub-zones, and information concerning the spatial distribution of the magnetic particles in the examination zone is extracted from these signals, so that an image of the examination zone can be formed. Such an arrangement has the advantage that it can be used to examine arbitrary examination objects—e.g. human bodies—in a non-destructive manner and without causing any damage and with a high spatial resolution, both close to the surface and remote from the surface of the examination object.
A similar arrangement and method is known from Gleich, B. and Weizenecker, J. (2005), “Tomographic imaging using the nonlinear response of magnetic particles” in nature, vol. 435, pp. 1214-1217. The arrangement and method for magnetic particle imaging (MPI) described in that publication takes advantage of the non-linear magnetization curve of small magnetic particles.
Known arrangements of this type have shown the disadvantage that the imaging resolution is limited due to the above mentioned magnetic selection field which has, due to its physical constraints, an anisotropic gradient strength. Therefore, the spatial selectivity is limited to only one spatial direction, whereas the imaging resolution is significantly weaker for all other spatial directions.
From U.S. Pat. No. 6,594,517 B1 a Magnetic Resonance Imaging (MRI) system is known, including three coils that are orthogonally arranged to each other. By controlling the electrical current through the coils a resultant magnetic dipole interacting with an external field is generated to produce a torque of the desired direction and magnitude.                An adaptation of such a system to MPI systems mentioned above is theoretically possible, but not advantageous since the structure and the arrangement of the coils used in MPI systems significantly differs from MRI systems. Furthermore, the selection field in an MPI system is, in contrast to a MRI system, not dynamic, but a static magnetic gradient field so that the physical principle disclosed in U.S. Pat. No. 6,594,517 B1 cannot be applied and also other physical phenomena occur. In contrast to U.S. Pat. No. 6,594,517 B1, in a MPI system, not the resulting torque is the parameter to be controlled, but instead, the shape and the accurate orientation of the generated selection field itself are the control parameters.        